Diagenesis of free and bound lipids in terrestrial detritus deposited in a lacustrine sediment

Recent sediments from an oligotrophic lake (Loch Clair) having uniform organic input for 2000 yr show changes in lipid abundance and composition, with increasing depth, attributed to diagenesis. Stability of free lipids decreases in the order n-alkanes, alkan-2-ones, sterols, n-alkanoic acids, n-alkanols, n-alkenoic acids. Diagenetic loss of shorter-chain homologues is complete within 400 yr. Stabilisation of bound relative to free lipids increases the proportion of the former with sediment age and reduces loss of shorter-chain bound homologues.In an eutrophic lake (Cross Mere), shorter-chain free and bound sedimentary lipids show increased abundance compared with Loch Clair. The relative importance of higher input of shorter-chain lipids derived from aquatic detritus, and slower initial diagenesis due to the anoxic hypolimnion, as causative factors for this difference between lake types cannot yet be assessed.